Process and apparatus for removal of volatile matter by electrical resistance heating

ABSTRACT

Volatile matter can be removed from material containing volatile matter removable by heat, e.g., coal and coke by delivering the material to a hearth so as to form a bed, touching the bed with downwardly projecting members disposed above the hearth, e.g., rabbles, moving the hearth and rabbles in relation to each other so as to cause movement of said material from the point of delivery of said material onto said hearth toward point of exit from said hearth, imposing an electrical potential between a point on the projecting members and a spaced point in the bed of material so as to cause heating by electrical resistance and thus remove at least a portion of the volatile matter. Preferably, the volatile matter is oxidizable and can be oxidized within a chamber enclosing the hearth so as to deliver additional heat to the bed causing additional devolatilization.

United States Patent Oleszko [4 Mar. 28, 1972 [s41 PROCESS AND APPARATUSFOR REMOVAL OF VOLATILE MATTER BY ELECTRICAL RESISTANCE HEATING [72]Inventor: Thaddeus J. Oleszko, Neuotting, Germany [73] Assignee:Marathon Oil Company, Findlay, Ohio [22] Filed: Oct. 6, 1969 211 Appl.No.: 866,790

[52] [1.8. CL ..202/2l6, 202/265, 202/269, 201/19, 201/33, 13/2, 13/23[51] Int. Cl. ..Cl0b 1/00, C10b 7/20, 801d 3/00, 1105b 11/00, C10b19/00, 1105b 3/60 [58] Field otSearch ..l3/2,20,21,23,34,25,9,

[56] References Cited UNITED STATES PATENTS 1,225,396 5/1917 Benjamin..201/19 X 1,806,027 5/1931 Smalley ..13/2 3,459,867 8/1969 Estes ..l3/93,475,286 10/1969 Kemmerer, Jr. et a1. ..201/33 X 1,384,878 7/1921Wingett ..202/l17 X 1,449,834 3/1923 Pehrson ..13/21 1,680,630 8/1928Okell ..13/23 2,127,542 8/1938 Stitzer ..201/l9 COKE SOAKING PIT2,448,886 9/1948 Hopkins ..l3/23 X 1,634,479 7/1927 Wickenden et a1......13/21 X 2,676,006 4/ 1954 Martin ..263/26 3,025,385 3/1962 Tanaka.....l3/20 X 3,227,627 1/1966 Asquini.... 201/32 X 3,448,012 6/1969Allred ...201/33 X 3 ,470,068 9/ 1969 Kemmerer ..24/3 3 PrimaryExaminer-Norman Yudkofi Assistant Examiner-G. 'J. Sofer Attorney-JosephC. Herring, Richard C. Willson, Jr. and Jack L. l-lummel [57] ABSTRACTVolatile matter can be removed from material containing volatile matterremovable by heat, e.g., coal and coke by delivering the material to ahearth so as to form a bed, touching the bed with downwardly projectingmembers disposed above the hearth, e.g., rabbles, moving the hearth andrabbles in relation to each other so as to cause movement of saidmaterial from the point of delivery of said material onto said hearthtoward point of exit from said hearth, imposing an electrical potentialbetween a point on the projecting members and a spaced point in the bedof material so as to cause heating by electrical resistance and thusremove at least a portion of the volatile matter. Preferably, thevolatile matter is oxidizable and can be oxidized within a chamberenclosing the hearth so as to deliver additional heat to the bed causingadditional devolatilization.

13 Claims, 5 Drawing Figures SO-ROTARY DISCHARGE TABLE SHEET 1 OF 4PATENTED MAR 2 8 I972 INVENTO? PATENTED m8 I912 ATTORNEY PATENTEQMAR28I972 SHEET 3 OF 4 Fig. 3-

/IVVENTO/? THADDEUS' J. OLESZKQ ATTORIVE SHEET H []F 4 AIR COOLINGCONDUITS RABBLES Fig.4

INVENTOR. THADDEUS J. OLESZKO PROCESS AND APPARATUS FOR REMOVAL OFVOLATILE MATTER BY ELECTRICAL RESISTANCE HEATING CROSS REFERENCES TORELATED APPLICATIONS BACKGROUND or THE INVENTION 1 Field of theInvention The present invention relates to the devolatilization ofmaterials by electrical resistance heating. The invention isparticularly applicable to coking of coal and to calcining of coal orpetroleum cokes. Among the pertinent United States Patent subclasses arethe following: 13-25; 201-19; 202-16; 202-18; 202-265; 202-270; and263-21.

2. Description of the Prior Art British patent 1,055,857, equivalent toU.S. Pat. 'No. 3475286, teaches apparatus comprising a hearth andprojecting members, which apparatus is adaptable to the practice of thepresent invention. This patent teaches nothing concerning resistanceheating of the bed. U.S. Pat. No. 3,227,627 and Ser. No. 613,145, filedFeb. I, 1967, now U.S. Pat. No. 3448012, both also teach apparatusadaptable to the practice of the present invention, but do not teach anysort of resistance heating. U.S. Pat. No. 2,127,542 shows a process forcarbonizing coal by passing an electrical current between electrodeslocated in contact with a charge of coal. U.S. .Pat. No. 1,680,630 toOkell teaches an electrical resistance furnace in which one oftheelectrodes rotates in order to agitate the material in the furnace bymeans of gas discharged from orifices within the electrode. None of thisprior art shows projecting members which fulfill the dual function ofacting as electrodes and also serve to move the material between theentrance point to the hearth and the exit point from the hearth.

SUMMARY 1. General Statement of the Invention The invention involves theresistance heating of a bed of material which contains volatile matterremovable by heat, which material has limited conductivity toelectricity. This resistance heating is accomplished by imposing apotential between a downwardly projecting member which touches the bedand a point on the bed spaced away from the member. This electricalheating is relatively localized and, for a relatively short time, raisesthe temperature of the material lying near the pointat which thedownwardly projecting member, e.g. rabble or plow is contacting the bed.The quality of calcined coke, e.g. the grain density and the coefficientof thermal expansion of the graphite resulting from graphitization ofthe calcined coke, has been found to be dependent upon the maximumtemperature to which the coke has been raised during calcination. Thus,premium quality coke must be raised to temperatures generally in excessof 2,300 F, and preferably in excess of 2,600 F. This can beaccomplished in apparatus such as that taught by the first threereferences mentioned in the above Description of the Prior Art. Suchapparatus accomplishes the heating of the material to be devolatilizedby means of oxidation either of auxiliary fuel, e.g. natural gassupplied in burners, or by the oxidation of a portion of the volatilematter itself in instances where such volatile matter is oxidizable.This oxidation is accomplished within the chamber generally locatedabove the hearth and having walls which are adapted to reflect heat andto deliver heat to the bed of material laying on the hearth. However,where the material is to be calcined to a high grain density andtherefore must be raised to temperatures of 2,400 F. or more, the archtemperatures (the temperatures at the walls of the chamber which aregenerally the maximum temperatures within the chamber), must be at least2,700 to 3,000 F. Such temperatures require relatively expensive specialhigh-temperature refractories to be used in the construction of thechamber walls. The present invention permits localized additionalheating by electricity to be applied to each portion of the bed for ashort time interval. Therefore, the present invention pennits increasingof the maximum temperature to which the material being calcined issubjected without increasing the arch temperature. By permitting lowerarch temperatures, the invention permits the use of less expensivelower-temperature refractory materials in the construction of thechamber. 7

Because the downwardly projecting members, e.g. plows or rabbles of theinvention can be set to project deeply into the bed and to contact orcome into close proximity with, every particle being calcined, theelectrical heating provides a uniformity which is not generally achievedby the radiant heating utilized in prior furnace installations. In suchradiant heating, the heat is delivered to the top of the bed byreflection downward from the walls and sides of the chamber. Thus thetop of the bed inherently receives more heat than those particles of thematerials which lie beneath the surface. In preferred embodiments of theinvention, the plow-like downward projecting members turn the bed overand simultaneously heat it by acting as electrodes for the electricalresistance heating.

A further problem in prior calcining apparatus was the difficulty inheating above about 2,500 F. by means of auxiliary heat supplied by gasburners. In many commercial instances, the oxidizable volatile matterwithin the material is sufficient to heat the material up totemperatures in the range of 2,200 F. to 2,400 F. However, to achievethe increased temperatures necessary to produce high-quality calcinedcoke, natural gas is sometimes burned in burners located within thechamber which encloses the hearth. Additional quantities of air must beinjected into the chamber in order to oxidize this gas. Since the air isgenerally available at a temperature in the range of 0 to 100 F., agreat deal of heat is utilized in increasing the temperature of thecombustion air up to the furnace temperature. Thus, in attempting toheat the bed above about 2,400 F. by means of auxiliary fuel gas, thepreheating of the additional air necessary to burn the fuel gas requiresapproximately percent of the heat given off by the fuel gas burned.Thus, 5 b.t.u.s of heating value of fuel gas must be burned to increasethe heat within the furnace by l b.t.u. The present invention avoidsthis inefficiency since electrical resistance heating is accomplishedwithout the addition of any air. Therefore, the air can be introduced insufficient amounts to burn the oxidizable volatile matter and to raisethe bed temperature to, for example, 2,200 F. without the addition ofexcessive amounts of oxidation air. The electrical resistance heating ofthe invention can then be utilized to raise the temperature of the bedup to the 2,500 F. or so required for the production of high qualitycalcined coke.

The combined electrode-plows of the present invention may be utilizedfor materials which yield only non-oxidizable volatile matter. In fact,the invention may be employed as the sole source of heating of thematerial in specialized circumstances, particularly where someconductive material is mixed with the coke to improve electricalproperties at lower temperatures. v

2. Utility of the Invention The present invention permits the productionof high quality cokes and other calcined materials. Coal can be coked,coal-coke can be calcined, delayed orfluid petroleum coke can becalcined, and other materials, carbonaceous or noncarbonaceous, can bedevolatilized by the apparatus and processes of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical section to afurnace embodying the invention.

FIG. 2 is a section showing details of the rabbles and rabble holdingmeans of FIG. 1.

FIG. 2A shows an alternate electrical circuit.

FIG. 3 is a schematic diagram showing details of the rotary hearth andthe rabbles of FIGS. 1 and 2.

FIG. 4 is similar to FIG. 2 but shows an alternate electrodearrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a furnaceaccording to the invention having a rotary hearth with an inner hearthsurface 11 sloping from the outer periphery downwardly to a centralaxially extending soaking pit l2 integral with and depending from thehearth 10. The rotary hearth 10 is supported on space rollers 13 mountedon a furnace frame 14 and is driven by a motor and a rack and piniondrive in conventional manner for rotary hearth furnaces. A curb 15extends vertically above the hearth surface 11 at its outer peripheryand carries a trough 16 with sand 17. A liquid may be used instead ofsand if preferred.

The furnace frame 14 carries roof beams 20 which support a refractoryroof having a central flue 22. Roof 21 has a depending wall 23 carryingflange 24 which extends into the sand 17 carried in trough 16 forming arotary sand seal between the roof 21 and hearth 10. The roof 21 isprovided with air ports 25 receiving air from duct 26 mounted on thefurnace frame 14. The ports 25 direct air downwardly towards thehearth-Side walls 23 of the roof are provided with ports 27 receivingair from duct 28 also mounted on the frame 14. The ports 27 direct airgenerally across the hearth in a radial direction. Burners 29 areprovided in the roof to bring the furnace to operating temperature. Afeed chute 30 passes through the roof 21 adjacent the side wall 23 andis provided with a vertically adjustable delivery end 31 extending to apoint adjustably selected to deliver a selected thickness of feed on thehearth surface 11. A radially extending U-shaped rabble pit 32 isprovided with electrical insulation 38 adapted to slidably receiverabbles 34. Rabbles 34 may be solid or of hollow plate-like structureswith inner vertical baffles for air or liquid cooling depending upon thetemperature involved. Each baffle is provided with inlet and outletcoolant conduits 37, which also act as support for the rabbles. Coolantsuch as raw air is delivered to the inlet and into the rabble 34 on oneside of the baffle, then under the baffle to the opposite side of therabble and out through the outlet pipe 37. Rabble carriers havingvertical adjustment screws at each end are provided so as to adjust thedistance between the end of the rabble and the hearth 11.

A rotary discharge table 50 is provided beneath the soaking pit 12 toreceive the output of the pit. A fixed discharge spout or plow 51 ismounted in frame 14 between the soaking pit l2 and the discharge table50. The spout 51 is provided with a peripheral trough 52 carrying sand53 into which a depending flange 54 on the soaking pit extends to form asand seal.

Referring now to the electrical aspects of the invention, the last threerabbles which the material encounters on its way toward the outlet 10,are attached to electric wires 81, 82, and 83, respectively, and areelectrically insulated from all of the other parts of the apparatus.Electrical insulating means is inserted into the water supply conduitsof these rabbles. Wires 81 and 83 are connected to one side of a sourceof direct current. Wire 82, connected to the middle of the threerabbles, is connected to the other side of the source of direct currentand such a potential difference is maintained as necessary to overcomethe resistance between the center and either of the end two of the threerabbles, to result in the necessary or desired temperature rise. Thevoltage is regulated by means of suitable electrical gear on thealternating current side of the rectifiers, or properly regulatedalternating current can be used without rectification as shown in FIG.2A. Alternative methods, such as connecting all of the rabbles to onepole of the direct current source and connecting electrodes placedwithin the bed (either depending from above or set into the bed) andconnected to the other pole could be used as shown in FIG. 4.

The furnace described above operates as follows. The burners 29 arefired to bring the furnace up to the desired chamber temperature whichdepends upon the nature of the material being devolatilized or calcined.The material to-be devolatilized or calcined, in this instance delayedpetroleum coke, is fed through feed chute 30 and is continuously spreadto the desired thickness, in this instance a bed depth of approximately6 inches and width along the outer periphery of hearth surface 11. Asthe hearth rotates, the material encounters the rabbles 34. Each set ofrabbles deflects material striking it into the next adjacent concentricring so that the flow of material from the periphery of the hearthsurface 11 to the soaking pit 12 is generally in spiral concentricrings, each of greater width so that as the rings become smaller thearea becomes greater providing a uniform depth. These concentric spiralrings are diagrammatically illustrated in FIG. 3, together with therelative position of each rabble with respect to such rings. Thevertical position of the rabbles determines the residual amount ofmaterial which is to be left on each ring as the hearth rotates. Therabbles tend to cause mixing and inversion of the bed several times asthe material moves downwardly from the hearth periphery to the soakingpit. This permits a more uniform heating and devolatilization andprovides a more uniform product.

In this embodiment, the arch temperature at the hottest point in thechamber is approximately 2,500 F. and the temperature measures at thetop of the coke bed is approximately 2,300 F. This is too low atemperature to provide a high grain density quality coke suitable forready conversion into graphite, e.g. graphite annodes forelectro-chemical uses.

As the coke encounters each of the first five rabbles itis turned overand subjected to heat radiated from the roof 21' and the side walls 23.Volatiles are removed through the action of this heat and these escapeinto the furnace chamber where they mix with air from ports 25 and 27causing combustion at a point spaced a distance above the surface of thecoke bed. This combustion is sufficient to maintain the arch temperatureof the furnace at the 2,500 F. temperature mentioned previously, andtherefore the burners 29 are turned'off.

The total residence time of an average particle of coke on the hearth isapproximately 25 minutes. As the average particle of coke contacts thesixth rabble, the first electrically heated rabble, its temperature isapproximately 2,300 F. As the bed is turned over by the sixth, seventh,and eighth rabbles electrical current flowing between the sixth andseventh and the seventh and eighth rabble heats the bed between theserabbles momentarily as each portion of the bed passes under the rabbles.The maximum temperature to which each particle is exposed averagesapproximately 2,500 F. This additional 200 temperature greatly improvesthe grain density of the finished product. The 200 F temperature boostconsumes approximately 50 kilowatt-hours per ton of calcined coketreated. In general, the electrical consumption will amount to roughly25 kilowatt-hours per ton per F. which the coke is raised above thetemperature in the general range of 2,500 F. Losses in conversion andlosses dependent on the various characteristics of the material beingcalcined can vary the energy requirement by several times. In general,the addition of 200 F. will require electricity costing from about $0.80to about $4.00 per ton, based on electric scale of $0.1 perkilowatt-hour. While this is a relatively expensive method of applyingheat, it is competitive on a cost basis with the inefficient applicationof heat by auxiliary burners at temperatures above 2,000" F. due to theenergy absorbed in preheating combustion air.

By using isolation transformers the rabbles lend themselves to beingused as electrodes with minimum insulation problems. The control ofnecessary power to give the proper temperature rise to the coke isaccomplished by the use of a saturatable core reactor. Either direct oralternating current can be used but the point is resistance heating as aprinciple. The electrical circuit diagrams of FIGS. 2 and 2a show twoalternate circuits but others will be evident to those skilled in theart.

MODIFICATIONS OF THE INVENTION It should be understood that theinvention is capable of a variety of modifications and variations whichwill be made apparent to those skilled in the art by a reading of thespecification and which are to be included within the spirit of theclaims appended hereto.

What is claimed is:

l. A continuous process for removing volatile matter from limitedlyelectrically conductive material such as coke or coal which yields suchvolatile matter under heat comprising continuously delivering suchmaterial through an entrance point to an annular hearth, moving saidmaterial toward a point of exit from said hearth by rabbles projectingdownward, disposed above the hearth and extending into the material,said projecting rabbles and said hearth moving relative to each other toturn and move the material, causing electrical resistance heating ofsaid material-at the point of contact of at least one of said projectingrabbles with the material lying on the hearth, said resistance heatingbeing caused by imposing an electrical potential between a conductiveportion of said projecting rabble and a point within said material lyingon said hearth which point is spaced from said projecting member,removing at least a portion of said volatile matter from said materialby means of said electrical resistance heating said volatile materialbeing oxidizable and additional heat being delivered to the material onsaid hearth by burning at least a portion of said oxidizable volatilematter above the surface of the material after it has been removed fromsaid material.

2. The process of claim 1 wherein the material is coke.

3. The process of claim 1 wherein the material is coal.

4. The process of claim 1 wherein the material is petroleum coke.

5. The process of claim 1 wherein the material is delayed petroleumcoke.

6. The process of claim 1 wherein the heat derived from the oxidation ofthe volatile matter is sufficient to heat the material lying on thehearth to a maximum temperature in the range of 2,000-2,600 F. andwherein said electrical resistance heating increases the maximumtemperature to which said material lying on the hearth is heated to atemperature above that obtainable by oxidation alone of said volatilematter in the apparatus being used.

7. Apparatus for treating limitedly electrically conductive materialsuch as coke or coal which contains volatile matter removable by heat'comprising an annular hearth, a central material outlet from saidhearth, means for delivering material to the hearth to form a bed ofmaterial upon the hearth, downwardly projecting rabbles disposed abovethe hearth and extending into said material, at least one of saidprojecting rabbles having at least a submerged portion thereofelectrically conductive, means for moving the hearth and projectingrabbles relative to each other, said projecting rabbles being disposedto move material on the hearth progressively toward the central materialoutlet during the relative movement between the hearth and saidprojecting rabbles, electrical means for imposing an electricalpotential between said electrically. conductive portion of said rabblewhere said rabble contacts said bed, and a point in said bed spaced fromsaid point where said bed contacts said projecting member saidhearthbeing located in a chamber, wherein at least a portion of saidvolatile matter is oxidizable and wherein means are provided for burningat least a portion of said oxidizable volatile matter within saidchamber and above the surface of said material so as to deliveradditional heat to said bed.

8. Apparatus of claim 7 wherein said material outlet includes a soakingpit having discharge means at the bottom thereof.

9. Apparatus of claim 7 wherein said projecting members compriserabbles. I

10. Apparatus of claim 7 wherein said projecting members are plow-shapedto promote turning over of the material as the material is progressivelyadvanced toward said material outlet. 11. Apparatus of claim 7 whereinsaid hearth 1S downwardly inclined in the direction from its point ofreceiving said material into said bed toward said material outlet so asto promote movement of the bed as it is progressively advanced towardsaid material outlet.

12. Apparatus of claim 7 wherein said hearth is substantially circularand wherein said projecting members are substantially radially arranged.

13. Apparatus of claim 12 wherein said projecting members areplow-shaped to promote turning over of the material as the material isprogressively advanced toward said material outlet, and wherein saidmaterial outlet is located substantially at the center of said circularhearth.

2. The process of claim 1 wherein the material is coke.
 3. The processof claim 1 wherein the material is coal.
 4. The process of claim 1wherein the material is petroleum coke.
 5. The process of claim 1wherein the material is delayed petroleum coke.
 6. The process of claim1 wherein the heat derived from the oxidation of the volatile matter issufficient to heat the material lying on the hearth to a maximumtemperature in the range of 2,000*-2,600* F. and wherein said electricalresistance heating increases the maximum temperature to which saidmaterial lying on the hearth is heated to a temperature above thatobtainable by oxidation alone of said volatile matter in the apparatusbeing used.
 7. Apparatus for treating limitedly electrically conductivematerial such as coke or coal which contains volatile matter removableby heat comprising an annular hearth, a central material outlet fromsaid hearth, means for delivering material to the hearth to form a bedof material upon the hearth, downwardly projecting rabbles disposedabove the hearth and extending into said material, at least one of saidprojecting rabbles having at least a submerged portion thereofelectrically conductive, means for moving the hearth and projectingrabbles relative to each other, said projecting rabbles being disposedto move material on the hearth progressively toward the central materialoutlet during the relative movement between the hearth and saidprojecting rabbles, electrical means for imposing an electricalpotential between said electrically conductive portion of said rabblewhere said rabble contacts said bed, and a point in said bed spaced fromsaid point where said bed contacts said projecting member said hearthbeing located in a chamber, wherein at least a portion of said volatilematter is oxidizable and wherein means are provided for burning at leasta portion of said oxidizable volatile matter within said chamber andabove the surface of said material so as to deliver additional heat tosaid bed.
 8. Apparatus of claim 7 wherein said material outlet includesa soaking pit having discharge means at the bottom thereof.
 9. Apparatusof claim 7 wherein said projecting members comprise rabbles. 10.Apparatus of claim 7 wherein said projecting members are plow-shaped topromote turning over of the material as the material is progressivelyadvanced toward said material outlet.
 11. Apparatus of claim 7 whereinsaid hearth is downwardly inclined in the direction from its point ofreceiving said material into said bed toward said material outlet so asto promote movement of the bed as it is progressively advanced towardsaid material outlet.
 12. Apparatus of claim 7 wherein said hearth issubstantially circular and wherein said projecting members aresubstantially radially arranged.
 13. Apparatus of claim 12 wherein saidprojecting members are plow-shaped to promote turning over of thematerial as the material is progressively advanced toward said materialoutlet, and wherein said material outlet is located substantially at thecenter of said circular hearth.